1. Field of the Invention
The present invention relates to document positioning and feeding apparatus for printers.
2. Description of Prior Art
High speed printers have been widely utilized in banks, credit companies and insurance companies. Users of high speed printers in these industries have specialized needs which include printing on different sizes and thicknesses of paper as encountered with checks, statement of account forms, and savings-books. In order to satisfy these needs it is necessary to provide a precise document feeding device, rather than the generally used pin wheel feeding device for uniformly sized printing stock. One form of precise feeding device consists of a feeding roller, like a typewriter roller, which cooperates with one or more pressure rollers as explained in U.S. Pat. No. 3,391,775. The printing stock is placed between the feeding roller and pressure rollers. Due to the friction between feeding roller and printing support, such printing stock can be fed in either direction by rotating the feeding roller, preferably by a "step" motor. However such a feeding device is not satisfactory particularly in printing multiple sheets of paper or printing papers having a non-uniform thickness. For example, if the contact friction between the multiple sheets is lower than the friction between a single sheet and the feeding roller, the single sheet tends to be advanced more than the other sheets in contact with the pressure roller. This produces a resisting action which opposes advancement thereby causing slippage which is prejudicial to the printing quality. In the case of printing stock of non-uniform thickness, for instance an open savings-book, such printing stock is pressed on the feeding roller by the pressure roller only on the thicker part of the book thereby causing slanted non-uniform feeding and poor quality printing.